The invention relates to a display tube including a deflection unit which comprises a coil support, an inner (line) deflection coil, an outer (field) deflection coil, a yoke ring and at least one plate-shaped metal correction means arranged within the outer (field) deflection coil.
A display tube of this type may be used in monochrome, color and projection television, in data display apparatus and in other apparatus in which cathode ray tubes are used.
Upon energization, the deflection unit generates magnetic deflection fields so as to deflect electron beams generated in the display tube for forming a picture on the display screen of the display tube. To influence the distribution of the field deflection field, it is common practice to arrange a correction means made of thin, soft-magnetic sheet material within the field deflection coil, for example, for improving the convergence.
In some cases it appears that an unwanted sound which is irritating to a user is caused during picture display.